Provide a serial "thread pool" for use in the tasking #6113

Job	Run time
CI-Rocm-HIP (hipcc, Release, hip, serial)	38m 28s
CI-Cuda-Host (g++, Release, cuda, serial)	44m 21s
CI-Rocm-HIP (hipcc, Release, hip, mpi)	38m 29s
CI-Cuda-Host (g++, Release, cuda, mpi)	43m 20s
CI-Rocm-HIP (hipcc, DbgNoSym, hip, serial)	31m 41s
CI-Cuda-Host (g++, Release, host, serial)	11m 47s
CI-Rocm-HIP (hipcc, DbgNoSym, hip, mpi)	31m 25s
CI-Cuda-Host (g++, Release, host, mpi)	11m 36s
CI-Cuda-Host (g++, DbgNoSym, cuda, serial)	36m 43s
CI-Cuda-Host (g++, DbgNoSym, cuda, mpi)	37m 54s
CI-Cuda-Host (g++, DbgNoSym, host, serial)	8m 19s
CI-Cuda-Host (g++, DbgNoSym, host, mpi)	8m 27s
CI-Cuda-Host (clang++-15, Release, cuda, serial)	30m 18s
CI-Cuda-Host (clang++-15, Release, cuda, mpi)	31m 20s
CI-Cuda-Host (clang++-15, Release, host, serial)	10m 35s
CI-Cuda-Host (clang++-15, Release, host, mpi)	11m 17s
CI-Cuda-Host (clang++-15, DbgNoSym, host, serial)	7m 59s
CI-Cuda-Host (clang++-15, DbgNoSym, host, mpi)	8m 0s
	7h 21m 59s

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